Photomask features with interior nonprinting window using alternating phase shifting

ABSTRACT

Aspects of the present invention provide for a novel photomask for patterning features for an integrated circuit, the photomask including masked features having interior nonprinting windows. In some embodiments, the interior nonprinting window is an alternating phase shifter, while the area surrounding the masked features transmits light unshifted. In other embodiments, the interior nonprinting window transmits light unshifted, while the area surrounding the masked features is an alternating phase shifter. Thus any arrangement of features can be patterned with no phase conflict.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of Chen, U.S. patent applicationSer. No. 10/728,436, “Photomask Features with Interior NonprintingWindow Using Alternating Phase Shifting,” filed Dec. 5, 2003, owned bythe assignee of the present invention and hereby incorporated byreference.

BACKGROUND OF THE INVENTION

The invention relates to a method for patterning fine features forsemiconductor devices using an alternating phase shifting mask.

Patterned features making up integrated circuits are conventionallyformed using photolithography and etch techniques. A photomask, whichtransmits light in some areas and blocks it in others, is formed, theblocking areas corresponding to the pattern to be formed on the wafersurface (or its inverse.) The surface to be patterned, for example asemiconductor or dielectric layer, is covered with a layer ofphotoresist, a photoreactive material. Light is projected onto thephotoresist surface using the photomask, selectively exposing areas ofphotoresist. The wafer is then subjected to a developing process, inwhich exposed photoresist (or unexposed photoresist, in the case ofnegative photoresist) is removed, leaving patterned photoresist behind.

The remaining patterned photoresist then typically serves to protectunderlying material during a subsequent etch process, creating featuresin the same pattern as the remaining photoresist.

Over the years integrated circuits have become denser and patternedfeatures smaller. As projected features become smaller, the limits ofresolution are reached and it becomes more difficult to project patternswith sharp edges. Poor resolution can lead to incomplete patterning andto incomplete etching or overetching, causing device flaws.

Alternating phase shifters, which invert the phase of light in someareas of the photomask, increasing contrast in light intensity at thephotoresist surface, are a powerful tool to improve resolution andsharpen edges.

The use of alternating phase shifters in photomasks, however, hasdisadvantages. When alternating phase shifters are used, projected lightis either incident, in what will be called zero degree phase, orinverted, in what will be called 180 degree phase (this is sometimesalso called π phase.) As will be more fully described, as conventionallyused, light in opposite phases must be transmitted on opposite sides ofan obscured area. The configuration of some patterns leads to phaseconflicts, in which rules dictate that the same area must see light ofopposite phases. To date, this has meant that use of alternating phaseshifters has been limited to only certain types of patterns.

Alternating phase shifters also typically require use of a trim mask,adding extra cost and processing time.

There is a need, therefore, to improve flexibility in the use ofalternating phase shifters in photomasks.

SUMMARY OF THE INVENTION

The present invention is defined by the following claims, and nothing inthis section should be taken as a limitation on those claims. Ingeneral, the invention is directed to an improved method for usingalternating phase shifters in a photomask for photolithography.

A first aspect of the invention provides for a photomask for patterningfine features comprising a first masked feature; a first transmittingnonprinting window substantially entirely enclosed within a perimeter ofthe first masked feature; and a first transmitting area substantiallyentirely surrounding the perimeter of the first masked feature in theplane of the photomask, wherein light transmitted through the firstwindow, after transmission through the first window, is in a firstphase, and light transmitted through the first transmitting area, aftertransmission through the first transmitting area, is in a second phasesubstantially opposite the first phase.

A related aspect of the invention provides for a photomask forpatterning fine features comprising a first nonprinting alternatingphase shifter wherein light transmitted through the photomask reaching aphotoresist surface substantially entirely within a perimeter of aprojected photoresist feature is in a first phase, and light reaching aphotoresist surface outside and in proximity to the perimeter of theprojected photoresist feature, on all sides of the projected photoresistfeature, is in a second phase substantially opposite the first phase.

Another aspect of the invention provides for a patterned feature on asemiconductor device, said patterned feature patterned from a maskedfeature in a photomask, said photomask comprising a transmittingnonprinting window, the window substantially entirely enclosed within aperimeter of the masked feature; and a transmitting area, thetransmitting area substantially entirely surrounding the perimeter ofthe masked feature in the plane of the photomask, wherein either thewindow or the transmitting area comprises an alternating phase shifter.

A preferred embodiment of the invention provides for a plurality ofpatterned features on a semiconductor device, said features patternedfrom masked features in a photomask, each of said masked featurescomprising a nonprinting window substantially entirely enclosed within aperimeter of the masked feature, and each of said masked featuressubstantially entirely surrounded in the plane of the photomask by acommon transmitting area, wherein either the window or the transmittingarea comprises an alternating phase shifter.

A related embodiment of the invention provides for a photomask forpatterning fine features comprising a first nonprinting transmittingwindow substantially entirely enclosed within a perimeter of a firstmasked feature; and a transmitting area substantially entirelysurrounding and in proximity to the perimeter of the first maskedfeature in the plane of the photomask, wherein the transmitting areaoperates as a first alternating phase shifter.

Yet another aspect of the invention provides for a method of forming aplurality of substantially evenly spaced pillars, the method comprisingforming a layer of a first material; depositing photoresist on the firstmaterial; patterning the photoresist using light having a wavelength ofabout 248 nm or more; etching the first material to form the pluralityof substantially evenly spaced pillars, the pillars having a pitchbetween about 220 and about 280 nm.

Each of the aspects and embodiments of the invention can be used aloneor in combination with one another.

The preferred aspects and embodiments will now be described withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a cross section of a portion of a conventional binaryphotomask.

FIG. 1 b shows the electrical field in the plane of the photomask forthe photomask of FIG. 1 a.

FIG. 1 c shows the light intensity at the surface of the photoresist forlight projected through the photomask of FIG. 1 a.

FIG. 2 a is a cross section of a portion of an alternating phaseshifting photomask.

FIG. 2 b shows the electrical field in the plane of the photomask forthe photomask of FIG. 1 a.

FIG. 2 c shows the light intensity at the surface of the photoresist forlight projected through the photomask of FIG. 1 a.

FIG. 3 illustrates phase assignment for a line-and-space pattern usingan alternating phase shifting mask.

FIG. 4 illustrates phase conflict for rectangular shapes arranged in agrid using an alternating phase shifting mask.

FIG. 5 shows the electrical field in the plane of the photomask when anunshifted region is immediately adjacent a shifted region.

FIGS. 6 a and 6 b illustrate imperfections in surrounding blockingmaterial.

FIG. 7 a is a cross-section of a photomask having a nonprinting interiorwindow comprising an alternating phase shifter within a masked feature.

FIG. 7 b is a cross-section of a photomask having a nonprinting interiorwindow wherein an alternating phase shifter substantially entirelysurrounds a masked feature.

FIG. 8 a shows successful phase assignment for rectangular shapesarranged in a grid pattern using nonprinting interior alternating phaseshifters.

FIG. 8 b shows the pattern of FIG. 8 a with inverse phase assignment.

FIG. 9 illustrates sizes of the nonprinting interior window, a maskedfeature, space between features, and pitch among masked features in aphotomask according to the present invention.

FIG. 10 is a plan view of a photomask having masked features withnonprinting interior windows according to the present invention forpatterning a line-and-space pattern.

FIG. 11 a illustrates possible shapes of nonprinting interior windows.

FIG. 11 b illustrates possible arrangements having more than onenonprinting interior window inside a single masked feature.

FIG. 12 illustrates the need for a trim mask in conventional alternatingphase shifting photomasks.

DETAILED DESCRIPTION OF THE INVENTION

As described earlier, as part of the process of forming patternedfeatures on an integrated circuit, light is projected through aphotomask onto a photoresist surface. A feature in a mask is projectedonto photoresist, then the photoresist feature is used to etch a featurein an underlying material, or in multiple layers of materials.

In this description, a masked feature will refer to a feature in aphotomask. Such a feature may be a line, a rectangle, or any othershape. A masked feature in a photomask substantially entirely orpartially obscures light, so that when light is projected through thephotomask, a corresponding feature in the photoresist is shielded fromlight, while the area outside of the obscured area is exposed. Thiscorresponding feature in photoresist will be called a projectedphotoresist feature. The projected photoresist feature will be roughlythe same shape as the masked feature, though corners on projectedphotoresist features tend to be rounded. Typically a linear dimension ina masked feature is four or five times the size of the correspondingdimension in the projected photoresist feature, depending on the stepperused.

Next the photoresist is developed, removing exposed photoresist andleaving only the projected photoresist features. (Note that negativephotoresist is also known in the art. When developed, the exposed areasof negative photoresist remain, while the obscured areas are removed.For clarity, this description will omit discussion of negativephotoresist. The skilled practitioner will appreciate that thetechniques of the present invention can be used with negativephotoresist as well, however.) The projected photoresist features arethen used to protect underlying layers in a subsequent processing step,such as a etch step.

The underlying feature created in the pattern of the projectedphotoresist feature will be called a patterned feature. A patternedfeature is roughly the same size and shape as the projected photoresistfeature used to create it, though many variables in the etch process maycause it to be larger, smaller, more rounded, etc. It will be understoodby those skilled in the art that the many varieties of etches make upthe conventional method to create a patterned feature from a projectedphotoresist feature, but that other methods can be imagined.

The simplest photomask is a binary photomask 10, shown in FIG. 1 a. Aplate of a transmitting material 12, for example quartz, makes up thebulk of the photomask. A blocking material 14, typically chromium, isformed in areas where light is to be obscured. FIG. 1 b shows theelectrical field in the plane of the photomask. The electrical field iseither positive (1.0), non-existent (0), or negative (−1.0). Where lightis transmitted it is in a first phase, here referred to as zero degreephase. Where light is blocked, there is no electrical field. (In FIGS. 1b and 1 c, the x-axis is horizontal position, corresponding withhorizontal position across the section of photomask shown in FIG. 1 a.)

FIG. 1 c shows the actual intensity distribution of light at thephotoresist surface. It will be seen that, due to interference effects,the edges of lighter and darker areas are not perfectly defined, andeven in the center of the obscured area, the intensity at thephotoresist surface is not zero. (A value of zero on the y-axis of FIG.1 c indicates zero intensity. The value of 1.0 is unitless andarbitrarily assigned, and the other values assigned relative to it. Thisis a standard representation of image intensity, as will be known tothose skilled in the art.)

FIG. 2 a illustrates an alternating phase shifting photomask 16. Thisphotomask is also made up of a plate of transmitting material 12, withregions of blocking material 14. In region 18, light is transmitted asin the binary mask. In region 20, however, the transmitting area 12 isetched such that light passing through it is shifted 180 degrees. Anarea of a photomask which inverts the phase of incident light, such astransmitting area 12, will be called an alternating phase shifter.

FIG. 2 b shows the electrical field in the plane of the photomask: Wherelight is transmitted with no phase shifting, it is in the first phase,zero degree phase. Where light is blocked, there is no electrical field.Where light is transmitted with phase shifting, it is in 180 degreephase, opposite the first phase. It will be understood that while lightin 180 degree phase is perfectly opposite light in zero degree phase,some small deviation can be tolerated; for example light can be in 179or 183 degree phase rather than 180 degree phase and have substantiallythe same effect. For purposes of this description, within ten degrees of180 degrees will be considered to be substantially opposite zerodegrees. (In FIGS. 2 b and 2 c, the x-axis is horizontal position,corresponding with horizontal position across the section of photomaskshown in FIG. 2 a.)

FIG. 2 c shows the intensity distribution of light at the photoresistsurface. While the electrical field shown in FIGS. 1 b and 2 b can beeither positive or negative, light intensity at the photoresist surfaceis only zero or positive, since the exposure intensity is proportionalto the square of the electric field. The transition from a positive to anegative electrical field in the photomask creates a forced zero oflight intensity reaching the photoresist surface, effectively causingdark areas to appear “darker”, and making edges sharper.

It will be seen that for an alternating phase shifting mask (this termwill be used to describe a photomask employing alternating phaseshifters), opposite phases should be used on opposite sides of anobscured region. Phase assignment—the process of determining which phaseis to be used in which transmitting area of the photomask—isstraightforward for some patterns, such as the alternatingline-and-space pattern pictured in FIG. 3. Zero degree phase is assignedto the left of line A, 180 degrees between lines A and B, zero degreesbetween lines B and C, etc.

Other patterns present difficulties, however. FIG. 4 shows a maskincluding rectangular masked features arranged in a grid pattern.Suppose all areas between rectangles in row A′ and in row B′ areassigned to 180 degree phase, and all areas between rectangles in row B′and in row C′ are assigned to 0 degree phase. Suppose further that allareas between rectangles in column A and in column B are assigned to 180degree phase, and all areas between rectangles in column B and in columnC are assigned to 0 degree phase.

It will be seen that in framed areas marked with a question mark (“?”)either phase could be appropriate, depending on whether the row rule orthe column rule is followed. If either phase is assigned, a region ofzero degree phase will be immediately adjacent a region of 180 degreephase. In the transition from zero degree phase to 180 degree phase, theelectrical field must pass through zero, as shown in FIG. 5. (The x-axison this figure again corresponds to horizontal position across thephotomask.) Where the electrical field is zero, the light intensity atthe photoresist surface will be zero, unintentionally creating a regionof unexposed photoresist, leading to a residual photoresist featureafter developing.

The present invention provides a solution to phase conflicts foressentially any photomask pattern. If a transmitting region in aphotomask is small enough, it will transmit light but will not “print”,i.e. it will not expose photoresist at the photoresist surface. In thepresent invention, masked features such as those shown in FIG. 4 includean interior nonprinting window. Light transmitted through thenonprinting window is in a first phase, while light transmitted througha transmitting area outside the masked feature is in a second phaseopposite the first phase. For example, the window may be an alternatingphase shifter, such that light transmitted through the window is in 180degree phase, while light outside the masked feature is in 0 degreephase. Alternatively, the window may transmit light in zero degreephase, while the transmitting area outside the masked feature is in 180degree phase. The window is described as “nonprinting” because itsdimensions are selected so that it will not print, i.e. such that lighttransmitted through it will not substantially expose photoresist withinthe perimeter of the corresponding projected photoresist feature.

When this description describes a window as “interior” it means that thewindow is substantially entirely enclosed within the perimeter of amasked feature. The transmitting area outside a masked featuresubstantially entirely surrounds the perimeter of the masked feature onall sides of the masked feature in the plane of the photomask.

When this description speaks of a material as “substantially entirely”surrounded by another material, it will be understood that small breaksor imperfections in the surrounding material may exist, eitheraccidentally or intentionally, while the result is the same as thoughthe break or imperfection did not exist. FIG. 6 a, for example,illustrates a nonprinting window A substantially entirely surrounded byblocking material B. In this case blocking material B has no breaks init. FIG. 6 b shows a similar nonprinting window B substantially entirelysurrounded by blocking material B. In 6 b, however, a small imperfectionexists in blocking material B. If the width of the imperfection is verysmall, for example 30 angstroms or less, the result when the photomaskis used will be the same as if the imperfection did not exist. Theembodiments shown in FIGS. 6 a and 6 b are considered to be equivalent,and both to fall within the scope of the invention.

Turning to FIG. 7 a, the surrounding regions of blocking material 14 andnonprinting window W make up a single masked feature F. Distance D₁ isselected such that window W is nonprinting. In transmitting area 22outside and in proximity to masked feature F, light is in zero degreephase. In region 24, light is shifted to 180 degree phase. Region 24 isan alternating phase shifter.

FIG. 7 b shows the opposite case. The surrounding regions of blockingmaterial 14 and nonprinting window W again make up a single maskedfeature F, and distance D₁ is selected such that window W isnonprinting. In transmitting area 26 outside and in proximity to maskedfeature F, light is shifted to 180 degree phase. In region 28, light isin zero degree phase. Region 26 is an alternating phase shifter.

Turning to FIG. 8 a, it will be seen that masked features with interiornonprinting windows, having light in one phase inside the masked featureand light in an opposite phase outside the masked feature, can beprinted with no phase conflict. Each masked feature F of FIG. 8 aincludes a window W, the window W comprising an alternating phaseshifter. Thus the windows W are assigned 180 degree phase. Thetransmitting area 34 commonly and substantially entirely surrounding themasked features F is assigned zero degree phase. The masked features Fin FIG. 8 a are constructed according to the cross-section of FIG. 7 a.

Alternatively, as in FIG. 8 b, each masked figure F of FIG. 8 b includesa window W. The window W transmits light in zero degree phase, whiletransmitting area 34 commonly and substantially entirely surrounding themasked features F is assigned 180 degree phase, and is an alternatingphase shifter. The masked features F in FIG. 8 b are constructedaccording to the cross-section of FIG. 7 b.

In short, the present invention allows patterning using an alternatingphase shifting mask for patterns other than line-and-space patterns,such as patterns in which features are substantially evenly spacedislands, such as the squares of FIGS. 8 a and 8 b. Random shapes in arandom arrangement can be patterned as well.

Accordingly, when using a photomask according to the present invention,light transmitted through the photomask reaching a photoresist surfacesubstantially entirely within a perimeter of a projected photoresistfeature is in a first phase, and light reaching a photoresist surfaceoutside and in proximity to the perimeter of the projected photoresistfeature, on all sides of the projected photoresist feature, is in theopposite phase. The same can apply to a plurality of features with nophase conflict. The phase shifted area can be either within or outsidethe masked features.

Monolithic three dimensional memory arrays such as the one taught inHerner et al., U.S. patent application Ser. No. 10/326,470, “An ImprovedMethod for Making High Density Nonvolatile Memory,” filed Dec. 19, 2002,hereby incorporated by reference, include a plurality of substantiallyevenly spaced pillars. These pillars can comprise polycrystallinesilicon, called polysilicon. The pillars are portions of memory cells,and the memory cells formed in the same patterning steps generally forma portion of a memory level at a first height above a substrate. Such amonolithic three dimensional memory array further comprises at least asecond memory level formed at a second height above the substrate, thesecond height different from the first height.

A photomask according to the present invention can advantageously beused to form pillars such as those described in Herner et al. FIG. 9shows an advantageous layout of masked features F comprising nonprintingwindows W, wherein light transmitted through the windows W is in a firstphase and light transmitted through the transmitting area T outside themasked features F is in a second phase opposite the first phase. Thefeatures F are preferably squares with edge D₂, and the windows arecentered squares with edge D₃, while the space between masked features Fis D₄. Pitch is the distance, in a repeating pattern, betweenoccurrences of the same edge, center, etc.; for example between centersof adjacent lines, or between the starting edge of one line and thestarting edge of the next. In FIG. 9, then, pitch is P. Thesubstantially evenly spaced pillars of Herner et al., which are formedusing a photomask like the one shown in FIG. 9 or in FIG. 8 a or 8 b,have a pitch of between about 220 nm and 280 nm, preferably about 260nm, and are patterned using light having a wavelength of 248 nm. Analternating phase shift mask paired with a quadrupole aperture is highlyeffective for patterning regularly spaced pillars.

It will be recalled that light is projected through a photomask having amasked feature to create a corresponding projected photoresist feature.The projected photoresist feature is then processed, typically byetching, to create a patterned feature. Pillars, for example the pillarsof Herner et al., are the patterned features created from the maskedfeatures F of FIG. 9. As noted earlier, while a patterned feature willbe roughly the same size as the projected photoresist feature from whichit was created, there is a scaling factor, typically about four or fivetimes, between the linear size of a projected photoresist feature andthe masked feature from which it was created; the masked feature islarger.

When describing dimensions in a photomask, it is usual to speak of thosedimensions in terms of the projected dimensions; i.e. rather thandescribing the size of a masked feature, one describes the size of theprojected photoresist feature it will create. This description willfollow this convention. For clarity, a masked dimension will bedescribed as “×S”, or multiplied by a projection scaling factor S. Forexample, a dimension of 200 nm in a projected photoresist feature willbe described as a dimension of 200 nm×S in a masked feature. If, forexample, the projection scaling factor S is four, the actual dimensionin the masked feature of 200 nm×S will be 800 nm. If the projectionscaling factor S is five, 200 nm×S will be 1000 nm.

Referring again to FIG. 9, to produce projected photoresist featureshaving a width of about 130 nm, dimension D₂ is about 130 nm×S.Dimension D₃ is between about 30 nm×S and about 90 nm×S, preferablyabout 50 nm×S. Dimension D₄ is about 130 nm×S. The projected photoresistfeatures are then etched to form the patterned features, which will bepillars, as described in Herner et al. As noted in Herner et al., whilethe masked feature is rectangular, the cross-section of the patternedfeature will tend to be substantially cylindrical. The dimensions givenhere assume that the light has a wavelength of 248 nm.

Masked features according to the present invention can also be used toform patterned lines, such as the conductors of Herner et al., which maycomprise tungsten. The masked features with interior windows could beformed as shown in FIG. 10. Dimension D₅, the width of the interiornonprinting window, is preferably between about 30 nm×S and about 70nm×S. Dimension D₆, the width of each line, is preferably between about100 and 130 nm×S. Dimension D₇, the width of the gap between lines, ispreferably between about 100 and 130 nm×S. As described earlier, thenonprinting window inside each masked feature line L is an alternatingphase shifter. Alternatively, the nonprinting window can transmit lightwithout inverting its phase, while the transmitting area 36 commonly andsubstantially entirely surrounding the masked feature lines L is analternating phase shifter.

An advantage of the present invention is that masked features of anyshape, in any arrangement, can be formed in a photomask usingalternating phase shifters with no phase conflict.

A nonprinting interior window of the present invention, which issubstantially entirely enclosed within the perimeter of a maskedfeature, can be any shape. Advantageous shapes may be polygonal, round,or frame, as shown in FIG. 11 a. Multiple windows can be used within asingle masked feature, as shown in FIG. 11 b.

If a nonprinting window within a masked feature in a photomask accordingto the present invention is too large, it will print, exposingphotoresist. If it becomes too small, it will no longer be effective(for light with wavelength of 248 nm, this limit is believed to bereached when the window's dimensions reach about 30 nm×S or less); inaddition, a very small window becomes increasingly difficult tofabricate.

The actual limit on the dimensions of window varies with its shape. Asthe skilled practitioner will understand, for example, a circle with aradius of 90 nm×S transmits more light than does a square with edges of90 nm×S. As a general guideline, however, it is advisable whenpatterning with light having a wavelength greater than or equal to about248 nm, either the largest dimension of the window should be 130 nm×S orless, or the smallest dimension should preferably be no more than about70 nm or less. When patterning with light having a wavelength greaterthan or equal to about 193 nm, either the largest dimension of thewindow should be 100 nm×S or less, or the smallest dimension should beno more than 50 nm×S or less.

For some irregular shapes, or shapes that are very large in onedimension, it may be most advantageous to use multiple nonprintingwindows, rather than single nonprinting window. It is envisioned thatall interior nonprinting windows for a single masked feature will mostadvantageously have the same phase; i.e. either all will or all will notbe alternating phase shifters.

This description has referred to blocking material surrounding thenonprinting interior window. In the present invention, blocking materialsubstantially entirely surrounds the window in the plane of thephotomask. A blocking material is one that transmits 15 percent or lessof incident light. The most commonly used blocking material is chromium,which is opaque. Other materials are used as well, however. One blockingmaterial that is advantageously used with the photomask of the presentinvention is molybdenum silicide. Molybdenum silicide transmits fromabout 6 to about 15 percent of incident light, and also reverses itsphase. When a masked feature includes a nonprinting interior windowwhich comprises an alternating phase shifter, the window substantiallyentirely surrounded in the plane of the photomask by blocking material,it may be advantageous to use molybdenum silicide as the blockingmaterial.

Other materials have similar properties, and can also be used in placeof molybdenum silicide. Possible blocking materials include tantalumsilicon oxide, among others.

The present invention provides an additional important advantage, inthat no secondary trim mask is required, as is usual when alternatingphase shifters are used. FIG. 12 shows a conventional layout, includingphase assignments, to create a line-and-space pattern. The phaseassignments for the spaces between lines alternate between zero and 180degrees, as shown, avoiding phase conflict.

The difficulty arises in regions 38, at the ends of the between-linespaces that have a phase of 180 degrees. Typically the area outside ofthe line-and-space pattern is zero degrees. Where the 180 degree phasespace and the zero degree surround meet, an unwanted residualphotoresist feature will be formed, as described earlier.Conventionally, such residual features are removed using a subsequenttrim mask. Use of an additional mask entails extra time and processingcost.

It has been shown that by placing opposite phases strictly within andoutside features, unintentional creation of such unwanted residualphotoresist features can be avoided. The line-and-space pattern of FIG.12 can be arranged as in FIG. 10 instead, with one phase interior to thelines, and the opposite phase both between the lines and in thesurrounding area outside of the line-and-space pattern, creating noresiduals.

Monolithic three dimensional memory arrays are described in Johnson etal., U.S. Pat. No. 6,034,882, “Vertically stacked field programmablenonvolatile memory and method of fabrication”; Johnson, U.S. Pat. No.6,525,953, “Vertically stacked field programmable nonvolatile memory andmethod of fabrication”; Knall et al., U.S. Pat. No. 6,420,215, “ThreeDimensional Memory Array and Method of Fabrication”; Lee et al., U.S.patent application Ser. No. 09/927,648, “Dense Arrays and Charge StorageDevices, and Methods for Making Same,” filed Aug. 13, 2001; Herner, U.S.application Ser. No. 10/095,962, “Silicide-Silicon Oxide-SemiconductorAntifuse Device and Method of Making,” filed Mar. 13, 2002; Vyvoda etal., U.S. patent application Ser. No. 10/185,507, “Electrically IsolatedPillars in Active Devices,” filed Jun. 27, 2002; Walker et al., U.S.application Ser. No. 10/335,089, “Method for Fabricating ProgrammableMemory Array Structures Incorporating Series-Connected TransistorStrings,” filed Dec. 31, 2002; Scheuerlein et al., U.S. application Ser.No. 10/335,078, “Programmable Memory Array Structure IncorporatingSeries-Connected Transistor Strings and Methods for Fabrication andOperation of Same,” filed Dec. 31, 2002; Vyvoda, U.S. patent applicationSer. No. 10/440,882, “Rail Schottky Device and Method of Making”, filedMay 19, 2003; and Cleeves et al., “Optimization of Critical Dimensionsand Pitch of Patterned Features in and Above a Substrate,” U.S. patentapplication Ser. No. 10/728,437, filed on Dec. 5, 2003 and issued asU.S. Pat. No. 7,423,304, all assigned to the assignee of the presentinvention and hereby incorporated by reference.

A monolithic three dimensional memory array is one in which multiplememory levels are formed above a single substrate, such as a wafer, withno intervening substrates. In contrast, stacked memories have beenconstructed by forming memory levels on separate substrates and adheringthe memory levels atop each other, as in Leedy, U.S. Pat. No. 5,915,167,“Three dimensional structure memory.” The substrates may be thinned orremoved from the memory levels before bonding, but as the memory levelsare initially formed over separate substrates, such memories are nottrue monolithic three dimensional memory arrays.

These monolithic three dimensional memory arrays are highly densestructures. Thus photomasks made according to the present invention canadvantageously be used to pattern any of the lines, pillars, or othertightly-packed structures formed at any level of these arrays.

The foregoing detailed description has described only a few of the manyforms that this invention can take. For this reason, this detaileddescription is intended by way of illustration, and not by way oflimitation. It is only the following claims, including all equivalents,which are intended to define the scope of this invention.

1. A photomask for patterning fine features comprising: a first maskedfeature comprising a perimeter of a blocking material which blockslight; a first transmitting nonprinting window substantially entirelyenclosed within the perimeter of the first masked feature; and a firsttransmitting area substantially entirely surrounding the perimeter ofthe first masked feature in a plane of the photomask, wherein lighttransmitted through the first transmitting nonprinting window, aftertransmission through the first transmitting nonprinting window, is in afirst phase, and light transmitted through the first transmifting area,after transmission through the first transmitting area, is in a secondphase substantially opposite the first phase.
 2. The photomask of claim1 wherein the first phase is 180 degrees and the second phase is zerodegrees.
 3. The photomask of claim 2 wherein the first transmittingnonprinting window comprises a first alternating phase shifter.
 4. Thephotomask of claim 3, wherein the first masked feature further comprisesat least a second alternating phase shifter.
 5. The photomask of claim 3wherein the first alternating phase shifter is substantially entirelysurrounded in the plane of the photomask by the blocking material. 6.The photomask of claim 1, wherein the blocking material compriseschromium.
 7. The photomask of claim 1, wherein the blocking materialcomprises molybdenum silicide.
 8. The photomask of claim 1 wherein thefirst phase is zero degrees and the second phase is 180 degrees.
 9. Thephotomask of claim 8 wherein the first transmitting area comprises analternating phase shifter.
 10. The photomask of claim 9 wherein thefirst transmitting nonprinting window is substantially entirelysurrounded in the plane of the photomask by the blocking material. 11.The photomask of claim 10 wherein the blocking material compriseschromium.
 12. The photomask of claim 1 wherein a largest dimension ofthe first transmitting nonprinting window is less than about 130 nmtimes a projected scaling factor and wherein light projected through thephotomask has a wavelength of about 248 nanometers or more.
 13. Thephotomask of claim 1 wherein the largest dimension of the firsttransmitting nonprinting window is less than about 100 nm times aprojected scaling factor and a wavelength of light projected through thephotomask mask is greater than about 193 nanometers.
 14. The photomaskof claim 1, wherein the first transmitting nonprinting window has apolygonal, round, or frame shape.
 15. The photomask of claim 1 furthercomprising: a plurality of masked features, wherein the plurality ofmasked features includes the first masked feature, each of the pluralityof masked features comprises a respective perimeter of blocking materialwhich blocks light, and comprises a transmitting, nonprinting windowsubstantially entirely enclosed within the respective perimeter of themasked feature; the first transmitting area commonly and substantiallyentirely surrounding the masked features in the plane of the photomask,wherein for each masked feature, light transmitted through thetransmitting, nonprinting window, after transmission through thetransmitting, nonprinting window, is in the first phase, and lighttransmitted through the transmitting area, after transmission throughthe transmitting area, is in the second phase.
 16. The photomask ofclaim 15 wherein the plurality of masked features are substantiallyevenly spaced islands.
 17. The photomask of claim 15 wherein theplurality of masked features are substantially parallel, substantiallyevenly spaced lines.
 18. The photomask of claim 15, wherein eachtransmitting nonprinting window is a square centered within therespective perimeter, and the respective perimeter is square.
 19. Thephotomask of claim 1, wherein the first transmitting nonprinting windowextends throughout an area which is enclosed by the perimeter.
 20. Thephotomask of claim 19, wherein the first transmitting nonprinting windowis a square centered within the perimeter, and the perimeter is square.21. The photomask of claim 19, wherein the first transmittingnonprinting window is a rectangle centered within the perimeter, and theperimeter is rectangular.
 22. The photomask of claim 19, wherein thefirst transmitting nonprinting window is a circle centered within theperimeter, and the perimeter is square.
 23. The photomask of claim 19,wherein the first transmitting nonprinting window is adjacent to theperimeter, inside the perimeter, and the first transmitting area isadjacent to the perimeter, outside the perimeter.
 24. A photomask forpatterning fine features, comprising: a first nonprinting alternatingphase shifter adjacent to a perimeter of blocking material which blockslight, wherein: light transmitted through the photomask reaching aphotoresist surface substantially entirely within a perimeter of aprojected photoresist feature is in a first phase, and light reaching aphotoresist surface outside and in proximity to the perimeter of theprojected photoresist feature, on all sides of the projected photoresistfeature, is in a second phase substantially opposite the first phase.25. The photomask of claim 24 wherein the first phase is 180 degrees andthe second phase is zero degrees.
 26. The photomask of claim 24 whereinthe perimeter is a perimeter of a first masked feature, and the firstnonprinting alternating phase shifter is substantially entirely enclosedwithin the perimeter of the first masked feature, and extends throughoutan area which is enclosed by the perimeter.
 27. The photomask of claim26 wherein the first nonprinting alternating phase shifter is surroundedin a plane of the photomask by the blocking material.
 28. The photomaskof claim 24, wherein the blocking material is chromium.
 29. Thephotomask of claim 24, wherein the blocking material is molybdenumsilicide.
 30. The photomask of claim 26 further comprising a pluralityof masked features, each comprising an alternating phase shifter withina perimeter of blocking material of each masked feature, eachalternating phase shifter extending throughout an area which is enclosedby the perimeter of blocking material.
 31. The photomask of claim 24wherein the first phase is zero degrees and the second phase is 180degrees.
 32. The photomask of claim 31 further comprising: a firstnonprinting window substantially entirely enclosed within the perimeter,and extending throughout an area which is enclosed by the perimeter, andsurrounded in a plane of the photomask by the blocking material, wherethe first nonprinting alternating phase shifter substantially entirelysurrounds the perimeter in a plane of the photomask.
 33. A photomask forpatterning fine features comprising: a first masked feature comprising aperimeter of a blocking material which blocks light; and a firstnonprinting alternating phase shifter which is substantially entirelyenclosed within the perimeter of the first masked feature and extendsthroughout an area which is enclosed by the perimeter.
 34. The photomaskof claim 33 wherein light transmitted through the first phase shifter isin a phase of 180 degrees.
 35. The photomask of claim 33 wherein thelargest dimension of the first nonprinting alternating phase shifter isless than about 130 nanometers times a projected scaling factor andwherein light projected through the photomask has a wavelength of about248 nanometers or more.
 36. The photomask of claim 33 wherein thelargest dimension of the first nonprinting alternating phase shifter isless than about 100 nanometers and a wavelength of light projectedthrough the photomask is greater than about 193 nanometers.
 37. Thephotomask of claim 33 wherein the first masked feature further comprisesat least a second alternating phase shifter.
 38. The photomask of claim33 wherein the first nonprinting alternating phase shifter has apolygonal, round, or frame shape.
 39. The photomask of claim 33 furthercomprising a plurality of masked features, wherein each of the pluralityof masked features includes a respective perimeter of a blockingmaterial which blocks light, and each of the plurality of maskedfeatures comprises an alternating phase shifter substantially entirelyenclosed within the respective perimeter.
 40. The photomask of claim 39wherein the plurality of masked features are substantially evenly spacedislands.
 41. The photomask of claim 39 wherein the plurality of maskedfeatures are substantially parallel, substantially evenly spaced lines.42. A photomask for patterning fine features comprising: a firstnonprinting transmitting window substantially entirely enclosed within aperimeter of a first masked feature, and extending throughout an areawhich is enclosed by the perimeter, where the perimeter comprises ablocking material which blocks light; and a transmitting areasubstantially entirely surrounding and in proximity to the perimeter ofthe first masked feature in a plane of the photomask, wherein thetransmitting area operates as a first alternating phase shifter.
 43. Thephotomask of claim 42 wherein light transmitted through the first windowis not phase shifted relative to incident light.
 44. The photomask ofclaim 43 wherein the first nonprinting transmitting window issubstantially entirely surrounded in the plane of the photomask by theblocking material.
 45. The photomask of claim 42 wherein the largestdimension of the first nonprinting transmitting window is less thanabout 130 nanometers times a projected scaling factor and wherein lightprojected through the photomask has a wavelength of about 248 nanometersor more.
 46. The photomask of claim 42 wherein the largest dimension ofthe first nonprinting transmitting window is less than about 100nanometers and a wavelength of light projected through the photomask isless than 248 nanometers.
 47. The photomask of claim 42, wherein thefirst masked feature further comprises at least a second nonprintingtransmitting window.
 48. The photomask of claim 42, wherein the firstnonprinting transmitting window has a polygonal, round, or frame shape.49. The photomask of claim 42 further comprising a plurality of maskedfeatures, wherein: the plurality of masked features includes the firstmasked feature, each of the plurality of masked features comprises anonprinting transmitting window enclosed within a respective perimeterof the masked feature, and extending throughout an area which isenclosed by the respective perimeter, and the plurality of maskedfeatures are commonly and substantially entirely surrounded by thetransmitting area.
 50. The photomask of claim 49 wherein the pluralityof masked features are substantially evenly spaced islands.
 51. Thephotomask of claim 49 wherein the plurality of masked features aresubstantially parallel substantially evenly spaced lines.